Harassment from Husband and In-laws

My sister has been harassed from very early after the marriage. Husband stays in a different state and as promised she was never been sent to the husband and instead was kept at in-laws home and was being harassed for every simple thing at home. This was a hindu wedding with consent of both the parties. Even after multiple enquiries my sister was never been sent to live with her husband. And her husband either ignores our requests and calls or just gives a reckless reply. My sister has been forced to go through very mental trauma. She had tried to commit suicide at once and after intervention of police councelling he promised to take care of my sister. However he never called back again and the father-in-law threatened that we are harassing him. It has been over an year and still my sister was at her In-laws not with her husband. And after multiple attempts he took my sister to live with him however she was confined to house and was never allowed to go out or work. By looking at my sister's life my mother has become very sick and died of medical reasons. Now he left my sister at my home and sent a legal notice of husband harassment. How do we proceed in this situation.